Nitrometer



May 25, 1964 J. J. J. s'rAuNToN ETAL 3,134,649

NITROMETER Filed Jan. 3. 1961 ATTORNEYS.

United States Patent O 3,134,649 NITROMETER John I. J. Staunton, GakPark, Lewis Malter, Niles, Edgar H. Stephens, Glenview, and Robert H.Smith, Jr.,

Wheaton, Ill., assiguors to Coleman Instruments, Inc., a

corporation of Delaware Filed Jan. 3, 1961, Ser. No. 80,272 8 Claims.(Cl. 231-253) This invention relates to a gas absorption apparatusadapted for use in a nitrometer, for measuring a volume of nitrogen inthe analysis of nitrogen content by the Micro-Dumas method.

In analyzing for nitrogen content, a weighed sample is heated tocombustion in an enclosed tube. The products of combustion are swept bya stream of carbon dioxide through heated nely divided copper and copperoxide beds which remove unwanted components. The remaining carbondioxide and nitrogen are then conducted from the combustion train into apotassium hydroxide solution in a nitrometer. There they are passed as astream of tine bubbles through the solution to remove the carbondioxide, and the nitrogen gas accumulates at the top of the nitrometerwhere its volume subsequently may be determined.

The classical nitrometer, known as the Pregl nitrometer, consists of acaustic reservoir provided with a mercury seal in the bottom, and gasfrom the combustion train is introduced into the mercury and escapesinto the caustic. A levelling bulb filled with caustic is connected tothe caustic reservoir below the liquid surface level, and it serves toequalize the internal and external pressure during measurement of thevolume of nitrogen collected in a graduated tube above the reservoir. Astop-cock valve closes the top of the graduated tube, and nitrogen isvented therethrough after measurement. This device is bulky and involvesthe handling of an awkward levelling bulb. Careful control of bubbleysize and rate is required for the eective absorption of carbon dioxide,due to the poor dispersion of the entering bubbles. Bubbles of nitro gentend to stick to the mercury-caustic interface and to creep up the sidewall, and they must be dislodged to avoid error. Leakage occurs at thestop-cock. A substantial waiting period is required after combustion iscomplete, for complete carbon dioxide absorption, temperatureequalization, and drainage of caustic from the walls of the graduatedtube. These effects vary considerably with changes in manipulation ofthe levelling bulb and operating technique.

A new form of nitrometer which eliminated some of the defects wasdevised recently, as described in Microchemical Journal, vol. IV, pages43-54, 1960. A shorter, larger diameter caustic reservoir is providedwith a side gas inlet into the caustic, with the elimination of themercury seal. Instead, the gas inlet is provided with a Bunsen valve,formed by a slit in the side of a terminal rubber tube with a closedend. A magnet encased in Teiion is provided in the caustic reservoir,and it is operated as a magnetic stirrer, resting on the bottom of thereservoir beneath the Bunsen valve. A fixed side arm pressure equalizingvessel is connected to the reservoir and cornmunicates therewith belowthe liquid level. The gas collected above the reservoir is measured by acalibrated piston and cylinder or syringe, which is operated to bringthe caustic level in the reservoir back to a reference level after gasis introduced. The caustic in the reservoir is then level with thecaustic in the pressure equalizing vessel. Connection of the gasabsorption apparatus to the piston and cylinder measuring apparatus andto the combustion train is made through ground and waxed ball and sockettype joints.

The foregoing design eliminates the bulk and awkwardness of the Preglnitrometer, but it also suiiers from several disadvantages. Theeffectiveness of the stirrer is borderline, because it is too remotefrom the bubble stream. The Bunsen valve is hard to make and maintain,and tends to introduce error-producing contamination. The design isprone to leakage at the piston seal, at the joints, and at the Bunsenvalve. If the latter leaks, a pressure drop in the combusiton trainmight cause caustic to be drawn back through the system with disastrousresults. The joints are hard to make and break.

The present invention has for its object to provide a new and improvednitrometer and a gas absorption apparatus adapted for use therein, andin other applications, which overcome these and other priordisadvantages, and which are especially characterized by accuracy ofmeasurement, and ease and rapidity of operation.

Arr important object is to provide better breakup and dispersion of gasbubbles from the combustion train in the absorption apparatus and toprevent them from sticking in the apparatus, while increasing the timein the absorption medium.

Another object is to provide an absorption appartus which includes amercury seal, in which the gas bubbles are prevented from adhering tothe mercury-caustic interface.

An additional object is to provide central release of the gas into theaborption medium, together with uniform non-turbulent rotationalstirring of the medium and upward central 'helical travel of the gasbubbles.

A further object is to provide an apparatus which is not prone toleakage in operation, and which may be disconnected from the systemeasily and rapidly when operation is discontinued or at any other time.

These and other objects, advantages and functions of the invention willbe apparent from the specification and from the attached drawingsillustrating preferred embodiments of the invention, in which like partsare identified by like reference symbols in each of the views, and inwhich:

FIGURE 1 is a vertical sectional and elevational view of one embodimentof the new nitrometer;

FlGURE 2 is a fragmentary vertical sectional view of a modification ofthe gas absorption apparatus illustrated in FIGURE l; and

FIGURE 3 is a fragmentary vertical sectional view of another modifiedform of the gas absorption apparatus.

The present invention provides a number of improve` ments over theaforementioned nitrometer described in the Microchemical Journal. Thegas absorption apparatus is especially characterized by provision of anabsorption chamber adapted to serve as a caustic reservoir, a mercurychamber therebelow, a restricted passageway between the chambers, andmeans for releasing a stream of gas in the mercury chamber beneath thepassageway. Stirring means preferably are provided in the absorptionchamber above the passageway. The new construction is very effective inbreaking up and dispersing gas bubbles, preventing bubble adherence, andproducing rapid complete absorption of carbon dioxide and accumulationof the nitrogen gas. The construction provides a number of additionalsignicant advantages, as will appear from the description which follows.

Referring to the drawings, a nitrometer 10 is illustrated in FIGURE l,and it includesa gas absorption apparatus generally indicated by thenumeral 12 and measuring apparatus generally indicated by the numeral14. The absorption apparatus is connected by a conduit 16 to thecombustion train, not shown, wherein a sample is combusted and theproducts are removed by a stream of carbon dioxide according to theMicro-Dumas method.

The absorption apparatus 12 includes a cylindrical absorption chamber 18having a ground llat bottom 20, a circular vertical side wall 22, and anupwardly and inwardly inclined conical top wall 24. A central or axialintegral tubular neck 26 is provided on the top wall 24 of theabsorption chamber. It has a relatively narrow cylindrical bore 28 inits lower portion, and an enlarged upper cylindrical bore 30 commencingat a point 32 spaced above the chamber 18. The absorption chamber islled with potassium hydroxide, normally to a reference mark 34 on theside of the neck 26, in the lower portion thereof.

A cylindrical mercury chamber or well 36 is arranged below theabsorption chamber 18 in aligmnent therewith. The mercury chamberincludes a flat bottom 38, a circular side wall 40, and an upwardly andinwardly inclined conical top wall 42. The mercury chamber communicateswith the absorption chamber 18 at the bottom 20 thereof, and axially ofthe two chambers, through a restricted passageway or narrow tubularconduit 44 integral with the two chambers. Mercury is contained in thechamber 36, normally up to the bottom edge 46 of the restrictedpassageway.

A captive Teflon-covered cylindrical magnet stirrer 48 is contained inthe absorption chamber 18, and it includes a central peripheral rib 50.The stirrer spins on the rib acting as a pivot, about the vertical axisof the restricted passageway 44. The stirrer spin is stabilized by theground flat construction of the absorption chamber bottom 20, with nodragging at the ends of the stirrer or moving olf center. We have foundthat the magnet stirrer 48 can be driven from a driver magnet (notshown) rotated below the thickness of mercury contained in the well 36,taking advantages of the high resistivity of mercury with its resultinglow eddy current attenuation of the driving eld.

A vertically arranged pressure equalizing vessel 52 is fixed on the gasabsorption apparatus 12, by means of a connecting member 54 between thevessel and the absorption chamber 18. The vessel is open to theatmosphere or other source of known pressure at its upper end 56. It isfilled with potassium hydroxide solution to a normal upper liquidsurface level 58 in the same plane with the reference mark 34 on theabsorption chamber neck 26. The pressure equalizing vessel is connectedto and communicates with the absorption chamber by a tubular conduit 60.The conduit is connected to the lower end of the vessel, upwardlyinclined from the vessel to the absorption chamber, and connected to theabsorption chamber beneath the surface of the potassium hydroxideabsorption medium when contained in the chamber.

A gas inlet tube 62 is fixed on the absorption apparatus by means of aconnection 64 to the absorption chamber 18. The tube extends through theside wall 40 of the mercury well 36, to the central vertical axisthereof. The tube opens upwardly on the axis and beneath the restrictedpassageway 44, at a sharp edged horizontal delivery face 66. An armportion 68 of the gas inlet tube is immersed 'n1 the mercury 70.

The absorption chamber neck 26 is connected to a conduit 72 in themeasuring apparatus 14. The conduit provides an air buer between thecaustic and the piston and cylinder, described below. This connectionand a connection of the gas inlet tube 62 to the combustion trainconduit 16 are made by sealed joints 74 and 76, respectively. Each jointincludes a ball socket 78 having an upper peripheral flange 80, and atubular male joint member 81 received therein which includes a clampingflange 82 and a resilient O-ring seal 84 at its lower end. The O-ringsform reliably leak-proof joints with the ball sockets 78, and they areself-aligning and rapidly discon- 4 necting. The joints may be securedby conventional clamps 86 connected on the ange members 80 and 82 of thesocket and male member.

The measuring apparatus includes a calibrated piston and cylinder orsyringe 87. The cylinder consists of two tubular metal parts 88 and 89each threaded at one end and there joined by a threaded coupling 90, andthe cylinder is closed at the outer ends. A smooth surfaced metal pistonor plunger 91 is mounted in the cylinder for reciprocal longitudinalmovement. A seal ring 92 constructed of a resilient material such asneoprene or Teilon is clamped between the tubular parts, and it bears onthe surface of the plunger between its ends. The seal partitions thecylinder to provide a gas chamber 93 in one part 88, which communicatesthrough an opening 94 in the closed end of the part with the conduit 72leading to the absorption chamber neck 26. The system is vented by meansof a stop cock 104 in a branch line 105 connected to the conduit 72.

The piston 91. is driven by a micrometer screw 95 mounted in thecylinder head part 89. The screw is in threaded engagement with anadjustable micrometer nut 96 secured to the end of the piston. A guidepin 97 prevents the piston from turning. It is mounted on the side ofthe piston and moves together with the piston in a longitudinal slot 98in the side wall of the head part 89. rThe micrometer screw shaft issupported by a sleeve 99 which extends through the end wall 100 of thehead part 89. Collars 101 and 102 are secured on the sleeve adjacent tothe opposite sides of the end wall, to prevent the screw from movinglongitudinally. The screw is turned by an external digital dial 103, onwhich gas volume readings are made.

In operation with the apparatus of FIGURE 1, gas enters the combustiontrain through the submerged arm 68 of the gas inlet tube. Bubbles breakolf cleanly at the sharp delivery face 66 of the arm, with no tendencyof the bubbles to creep over and cling to side walls. The delivery tipis also clear and non-clogging.

The gas flow displaces the mercury in the gas inlet tube 62 and alsosome of the mercury in the well 36. This causes the mercury to rise inthe restricted passageway 44, to the top of the passageway and on linewith the bottom 20 of the absorption chamber at normal ilow rate. Theemerging bubbles shrink almost at once in the circulating mass ofabsorption medium and are forthwith torn apart and further dispersed bythe stirrer 48. The mercury level moves up and down in the passageway 44as each bubble is expelled.

In this manner, the gas bubbles rise straight through an interface ofsmall area between the mercury and the absorption medium, eliminatingthe tendency to stick at the interface and sweeping the interface clean.The pumping action of the mercury is a further safeguard againststicking of bubbles. With the bubbles broken up and dispersed asdescribed above, rapid and complete gas absorption is achieved.

Should the ilow rate increase, the interface remains the same, becausemercury is removed by stirrer action and driven to the bottom perimeterof the absorption chamber as indicated at 106 in FIGURE 3. At lower thannormal gas evolution rates, the mercury level may be lowered in therestricted passageway 44. The pumping action of the mercury due to thebubble flow maintains a circulation of fresh potassium hydroxide in thepassageway, so that carbon dioxide bubbles collapse immediately onleaving the interface and do not block the constriction.

A preferred exemplary construction of the restricted passageway 44 inthe construction illustrated is about 4 millimeters long and has aninternal diameter of about 4 millimeters. With a smaller diameter, theremay be a tendency to trap and coalesce bubbles at low ow rates. With alarger diameter, the self clearing characteirstics of the smallinterface between the mercury and the potassium hydroxide may bevitiated.

Should a large gas evolution rate be experienced commonly during earlystages of combustion followed by extended low rates thereafter, anincrease in eliiciency and elimination of the requirement for manualreturn of excess mercury to the well after a run may be effected in themanner illustrated in FIGURE 3. A perimeter groove or sump 107 isprovided around the bottom 20 of the absorption chamber, and it isconnected to the mercury well 36 by a mercury return tube 108. With thisconstruction, excess mercury will merely accumulate by centrifugalaction as indicated at 106, and the mercurycaustic interface level -willbe maintained near the top of the restricted passageway 44 for bestabsorption eiciency at both righ and low gas ow rates.

The stirrer 48 and its arrangement are especially important forproducing rapid gas absorption at high rates of flow. It is supported bythe absorption chamber bottom above the point of gas introduction, whichprovides greatly improved bubble breakup and dispersion. The stabilizingspin of the stirrer imparts a rotation to the absorption medium whichcauses the gas bubbles to follow a long upward helical path, shrinkingas they go, as indicated by the lines 199 in FIGURE 3. The travelincreases the available absorption time in the medium. The rotation ofthe medium also scrubs any clinging bubbles off the absorption chamberwall, causing them to move into the center of the medium adjacent thevertical axis of the absorption chamber by centrifugal vortex action.

The absorption chamber 18 is not encumbered by any drag-producingmembers, so that the rotation of the caustic absorption medium is notimpeded or broken up into undesirable turbulence. At the same time, thearm 68 of the gas inlet tube 62 which is immersed in the mercury 70prevents rotation thereof, to prevent wandering of the gas bubbles inthe mercury well 36. The upward inclination of the conduit 60 from thepressure equalizing vessel `52 to the absorption chamber 18 precludesthe trapping of gas bubbles in the conduit which was previouslyencountered. In the new construction, therefore, gas is delivered frombelow in the center of the apparatus with the elimination of factorstending to cause the bubbles to wander or be trapped by adhesion.

The enlarged bore 30 commencing at the point 32 in the absorptionchamber neck 26 functions very effectively to break any bubbles whichreach this point and prevent caustic from being swept up into themeasuring apparatus 14. This construction requires no waiting period fortemperature equalization before making a reading. When the nitrogen gashas accumulated over the caustic, the piston and cylinder 87 is operatedby the digital dial 103 to move the piston 91 and bring the causticlevel to the reference mark 34. The volume of nitrogen then is read onthe dial. The new construction reduces the analytical time as much asten to fifteen minutes below that required for the Pregl nitrometer. Theincreased speed coupled with increased accuracy and reduction ofcritical items of technique is of substantial importance in laboratoryoperations.

The mercury well 36 furnishes a protective seal against back flow intothe combustion train. This safeguard is augmented by the high gas inlettube 62 which extends upwardly in the apparatus and is secured to theabsorption chamber 18. The delivery tip 66 on the gas inlet tube remainsclear and open without the clogging tendencies of a valve device.

With any combustion train, a shut down for an extended period of timeresults in contraction of the gas in the system, which tends to draw thecontents of the nitrometer back through the system. Likewise, in theevent of a drop in temperature of the measuring apparatus 14, there maybe a tendency to draw caustic absorption medium into this apparatus. Thequick-disconnecting O-ring seal joints 74 and 76 enable the absorptionapparatus to be removed at any time and avoid these possibilities. Also,

spent caustic is easily-replaced, since the absorption apparatus readilycan be removed, and it is a free standing unit not subject to possibleleakage.

The stirrer 48 may be captive, which has the advantage that it isprotected from handling and is cleaned by the same chromic acid processused to clean the glass apparatus. This is important in preventingcontamination of the stirrer surface by grease or other material whichwill cause adhesion of bubbles that are difficult to dislodge. Thecaustic absorption medium can be poured from the apparatus when spent,the apparatus can be rinsed repeatedly, and fresh medium can be addedwithout losing a substantial amount of the mercury, which does notrequire replacement. The restricted passageway 44 serves to retain themercury.

Should other considerations make it advisable for a non-captive stirrerto be used, the embodiment of FIG- URE 2 may be employed. The pressureequalizing vessel 52' thereof has an enlarged bottom opening 110 whichenables the stirrer 48 to be removed therethrough. An enlarged conduit60 is provided which includes a downwardly inclined bottom wall 111merging with the bottom 20 of the absorption chamber. The wallinclination prevents mercury globules and associated gas bubbles frommoving too far into the conduit, and the mercury will return to theabsorption chamber 18. An upwardly inclined top wall 112 insures thatgas bubbles which enter the conduit 60' will return to the absorptionchamber. Also, the mercury reservoir can be lled through the pressureequalizing Vessel 52 if desired.

In the embodiment of FIGURE 3, the lower end of Y the conduit 60 leadingfrom the pressure equalizing vessel to the absorption chamber isconnected to the mercury well 36 by a mercury return leg or conduit 113.This leg serves to return any globules of mercury that may be swept intothe caustic conduit 60. The stirrer 48 is then captive, as in theembodiment of FIGURE 1.

The invention thus provides a compact nitrometer gas absorptionapparatus which 'functions Very rapidly and conveniently to performaccurate nitrogen analyses. The components of the apparatus combine toprovide rapid and complete breakup and dispersion of gas bubbles withoutadhesion of the bubbles to various parts of the apparatus, wtihresulting rapid and complete gas absorption. The prior causes ofinaccuracies, delays, leaks and backups have been obviated.

It will be apparent that various changes and modifications may be madein the preferred embodiments of the invention which are illustrated, andin the operation thereof, within the spirit and scope of the invention.It is intended that such changes and modications be included within thescope of the appended claims.

What we claim as new, and desire to secure by Letters Patent of theUnited States, is:

1. Gas absorption apparatus which comprises an absorption chamber, amercury chamber therebelow, a restricted passageway of small crosssection compared with the cross section of said chambers interconnectingsaid chambers for conducting gas to said absorption Ichamber, conduitmeans having an upwardly facing opening for releasing a stream of gasbubbles in said mercury chamber directly beneath said passageway, andstirring means in said absorption chamber directly above said passagewayfor breaking up gas bubbles entering said absorption chamber from saidpassageway.

2. Gas absorption apparatus which comprises an absorption chamber, amercury chamber therebelow, a restricted passageway of small crosssection compared with the cross section of said chambers interconnectingsaid chambers for conducting gas to said absorption chamber, conduitmeans having an upwardly facing opening for releasing a stream of gasbubbles in said mercury chamber directly beneath said passageway,stirring 'means in said absorption chamber directly above saidpassageway for breaking up gas bubbles entering said absorption chamberfrom said passageway, and a central tubular neck communicating with thetop of said absorption chamber having a restricted bore therethrough tobreak up any bubbles which reach said neck and to hinder liquid flowtherethrough.

3. Gas absorption apparatus which comprises an absorption chamber, amercury chamber therebelow, a restricted passageway of small crosssection compared with the cross section of said chambers interconnectingsaid chambers for conducting gas to said absorption chamber, conduitmeans having an upwardly facing opening for releasing a stream of gasbubbles in said mercury chamber directly beneath said passageway,stirring means in said absorption chamber directly above said passagewayfor breaking up gas bubbles entering said absorption chamber from saidpassageway, a pressure equalizing vessel xed on said apparatus, and'conduit means connecting said vessel and said absorption chamber andbeing inclined upwardly from said vessel to said chamber.l

4. In a nitrometer, gas absorption apparatus which comprises anabsorption chamber, a mercury chamber therebelow, a restrictedpassageway of small cross section compared with the cross section ofsaid chambers interconnecting said chambers for conducting gas to saidabsorption chamber, conduit means having an upwardly facing opening forreleasing a stream of gas bubbles in said mercury chamber directlybeneath said passageway, magnetically actuated stirring means in saidabsorption chamber directly above said passageway for breaking up gasbubbles entering said absorption chamber from said passageway, a centraltubular neck communicating with the top of said absorption chamberhaving a restricted bore therethrough, a pressure equalizing vessel xedon said apparatus, and conduit means connecting said vessel and saidabsorption chamber and being inclined upwardly from the vessel to thechamber.

5. The apparatus of claim 1 in which said mercury chamber is lilled withmercury at least to the lower end of the restricted passageway and saidabsorption chamber is filled with absorption medium to provide aninterface of small area between the mercury and the absorption medium.

6. Gas absorption apparatus which comprises an absorption chamber, amercury chamber therebelow, a restricted passageway of small crosssection compared with the cross section of said chambers interconnectingsaid chambers for conducting gas to said absorption chamber, a conduitdisposed within said mercury chamber and having an upwardly turned endwith a sharp delivery face directly beneath said passageway for cleanlyreleasing a stream of gas bubbles, and stirring means in said absorptionchamber directly above said passageway for breaking up gas bubblesentering said absorption chamber from said passageway.

7. Gas absorption apparatus which comprises an absorption chamber, amercury chamber therebelow, a restricted passageway of small crosssection compared with the cross section of said chambers interconnectingsaid chambers for conducting gas to said absorption chamber, conduitmeans having an upwardly facing opening for releasing a stream of gasbubbles in said mercury chamber directly beneath said passageway, saidabsorption chamber having a perimeter sump in the bottom thereof, anopening through the bottom of said sump to provide for draining mercuryfrom the sump back to the mercury chamber, and stirring means in saidabsorption chamber directly above said passageway for breaking up gasbubbles entering said absorption chamber from said passageway.

8. The apparatus of claim 7 which includes a pressure equalizing vesselXed on the apparatus, a conduit eX- tending downwardly from the bottomof said vessel to said mercury chamber, and a branch conduit extendingupwardly from said downwardly extending conduit at a point above the topof the mercury chamber to interconnect said downwardly extending conduitto the absorption chamber.

References Cited in the iile of this patent UNITED STATES PATENTS1,124,432 Heath Jan. 12, 1915 1,366,382 Heath Jan. 25, 1921 OTHERREFERENCES Gustin: Microchemical Journal, vol. IV, March 1960, pages43-54.

Gustin: Microchemical Journal, v01. I, pages -87, 1957.

1. GAS ABSORPTION APPARATUS WHICH COMPRISES AN ABSORPTION CHAMBER, AMERCURY CHAMBER THEREBELOW, A RESTRICTED PASSAGEWAY OF SMALL CROSSSECTION COMPARED WITH THE CROSS SECTION OF SAID CHAMBERS INTERCONNECTINGSAID CHAMBERS FOR CONDUCTING GAS TO SAID ABSORPTION CHAMBER, CONDUITMEANS HAVING AN UPWARDLY FACING OPENING FOR RELEASING A STREAM OF GASBUBBLES IN SAID MERCURY CHAMBER DIRECTLY BENEATH SAID PASSAGEWAY, ANDSTIRRING MEANS IN SAID ABSORPTION CHAMBER DIRECTLY ABOVE SAID PASSAGEWAYFOR BREAKING UP GAS BUBBLES ENTERING SAID ABSORPTION CHAMBER FROM SAIDPASSAGEWAY.